1. Field of the Invention
This invention relates to delay line systems based on propagation of light energy signals through an optical fiber.
2. Description of the Prior Art
In the prior art, various physical phenomena have been used to delay an electrical signal; for instance, for analog signals, the propagation of electrical signals in an electrical transmission line with lumped or distributed constants, the propagation of acoustic waves in solids or liquids, magnetic recording/read-out using tape, magnetic disc or drum, etc. Recent developments in the field of optical fibers have led to the design of delay lines utilizing the propagation of light signals in optical fibers. Such devices take advantages of known properties of optical fiber systems, such as very large bandwidth, insensitivity to electromagnetic noise, absence of crosstalk and security against message interception. However, proposed optical fiber delay lines are limited in performance and, in particular, the maximum obtainable delay is limited by a degradation in signal-to-noise ratio and bandwidth at the output of the system as the length of the fiber is increased.
Typical prior art optical delay line systems are shown in the patent and technical literature. U.S. Pat. No. 3,991,417 shows a fiber optic delay line system utilizing frequency (light color) discriminating reiteration.
The utility of fiber optic delay lines, and systems therefor, extends throughout the electronic arts. Two utilizations are described in U.S. patent applications Ser. No. 728,309, filed Sept. 30, 1976, and Ser. No. 597,417, filed July 21, 1975 now U.S. Pat. No. 4,028,702. Those patent applications are entitled, "MTI Canceller with Fiber Optic Delay Lines" and "Fiber Optic Phased Array Antenna System for RF Transmission", respectively, and are both assigned to the assignee of this application.
The manner in which the present invention improves upon the state of the art will be evident as this description proceeds.